Methyl-coenzyme M reductase (MCR) is the key enzyme involved in the production of methane by methanogenic archaea and its consumption by anaerobic methanotrophs (ANME). MCR is a multimeric complex composed of six different subunits arranged in a 2α, 2β, 2γ configuration that requires two molecules of its nickel-containing tetrapyrrole prosthetic group, coenzyme F430. Additionally, the α subunits of MCR house a variety of different post-translational modifications across both methanogens and ANME. In methanogens, MCR is encoded in a conserved mcrBDCGA gene cluster, which encodes accessory proteins McrD and McrC. These are believed to be involved in the assembly and activation of MCR, respectively. However, one or both accessory proteins are often omitted from the operon in other MCR-containing archaea as is the case in ANME. MCR knowledge is mostly limited to methanogens due to difficulties associated with large-scale cultivation of ANME and other MCR-containing archaea. Due to the complexity of MCR, studies on this enzyme are also largely limited to native enzymes. Developing methods for the detailed biochemical characterization ANME MCRs would be highly desirable since these enzymes are proposed to be optimized for methane oxidation and thus have immense potential for bioenergy and greenhouse gas mitigation applications. In addition to containing the necessary machinery for the production of an assembled and active MCR, model methanogens are easier to culture and have established genetic manipulation techniques, making them ideal candidates for the development of heterologous expression systems. Thus, here we sought to generate such a system for the study of various ANME MCRs in the methanogen, Methanococcus maripaludis. We report the successful expression and purification of an ANME-2d MCR, marking a significant step toward the development of a heterologous MCR expression system. Additionally, our attempts to purify various recombinant MCRs revealed the importance of including accessory proteins, particularly McrD, within expression constructs. Therefore, we also sought to functionally characterize McrD, which we show is likely an MCR chaperone that plays a key role in MCR maturation. Taken together, our work has provided key insights into MCR assembly as well as provided a foundation for the eventual development of MCR based biocatalytic systems to be used for methane mitigation strategies and bioenergy platforms. / Doctor of Philosophy / Life is divided into three domains known as Bacteria, Eukarya, and Archaea. Methanogens are anerobic microbes belonging to the domain Archaea, which can be found across a wide variety of oxygen deprived environments. These organisms can turn different carbon-containing compounds into energy and methane gas in a process known as methanogenesis. This results in roughly 90 billion tons of biologically produced methane, making methanogenesis a key point of interest for potential greenhouse gas mitigation. The methane-generating step of methanogenesis is performed by methyl-coenzyme M reductase (MCR), a large enzyme composed of two α subunits, two β subunits, and two γ subunits. Additionally, this enzyme harbors a nickel-containing cofactor which is responsible for catalyzing the difficult methane formation reaction. In addition to the MCR-encoding genes, MCR gene clusters contain two extra genes that encode accessory proteins, named McrC and McrD, which are believed to play an important role in the activation and the assembly of the enzyme, respectively. Relatives of methanogens known as Anerobic Methanotrophs (ANME) are a different type of archaea which consume methane by reversing methanogenesis in a process known as anerobic methane oxidation. Because of their ability to consume methane, there is a large interest in studying MCR from these organisms to potentially use it for methane mitigation strategies and for bioenergy applications to convert methane to more usable liquid fuels. However, due to the high difficulty of growing ANME in a lab setting, studying any biochemical processes from ANME is a difficult task. Luckily, genetic manipulation techniques are available for many methanogens, making them ideal candidates to study MCR from ANME organisms. In this work, we sought to develop a system to express and purify MCR from different methanogens and ANME in a methanogenic host, Methanococcus maripaludis. We also sought to understand the role and importance of accessory protein McrD, especially with respect to developing a proper expression system for MCRs. We were able to successfully express a ANME MCR in M. maripaludis and found that McrD is an important aspect to consider when expressing MCRs in a methanogen, although it is not essential for this protein to exist within the MCR gene cluster. This work sets the stage for the future biotechnological use of MCR for methane mitigation and bioenergy applications.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

Made available in DSpace on 2014-12-17T15:42:13Z (GMT). No. of bitstreams: 1 ValdeliceRS_TESE.pdf: 2586359 bytes, checksum: e3d9d5d8e2c97ad0990f43fd755545a2 (MD5) Previous issue date: 2010-11-26 / One of the main applications of methane is in the production of syngas, a mixture of hydrogen and carbon monoxide. Procedures used in this process are steam reforming, CO2 reforming, partial oxidation and autothermal reforming. The present study evaluated and compared the behavior of nickel catalysts supported on mixed oxides of cerium and manganese in the partial oxidation of methane with that of nickel catalysts supported on mixed oxides of cerium and zirconium. Mixed oxides of cerium and zirconium or cerium and manganese were synthesized using two different preparation methods, the polymeric precursor based on Pechini method and combustion reaction using a microwave. This was followed by impregnation with nickel content of 15 %. Samples were calcined at 300, 800 and 900 ?C and characterized by specific surface area (SSA), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR) and the reaction of partial oxidation of methane. The specific areas of samples decrease with the rise in calcination temperature and after nickel impregnation. Metal-cerium solid solution was formed and the presence of other manganese species outside the solid solution structure was confirmed in the compound with the highest amounts of manganese oxides showed. With regard to scanning electron microscopy, supports based on cerium and zirconium prepared by Pechini method exhibited agglomerated particles without uniform geometry or visible pores on the surface. However, compounds containing manganese presented empty spaces in its structure. Through synthesis by combustion reaction, morphology acquired independently of the proposed composition demonstrated greater porosity in relation to Pechini synthesis. Although catalysts were prepared using different synthesis methods, the insertion of nickel showed very similar reduction profiles (TPR). In relation to nickel catalysts supported on mixed oxide of cerium and zirconium, there is an initial reduction of NiO species that present certain interaction with the support. This is followed by the reduction of Ce4+ in Ce3+ surface, with subsequent bulk reduction. For catalysts containing manganese, a reduction of nickel oxide species occurs, followed by two stages of reduction for species Mn2O3 in Mn3O4 and Mn3O4 in MnO, with subsequent reduction of bulk. With respect to partial oxidation reactions, the nickel catalyst supported on mixed oxide of cerium and zirconium, prepared using the Pechini method, exhibited CH4 conversion of approximately 80 %, with conversion of 81 % when prepared by combustion. This behavior continued for 10 hours of reaction. Manganese content was also found to directly influence catalytic activity of materials; the greater the manganese oxide content, the faster deactivation and destabilization occurred in the catalyst. In both synthesis methods, the nickel catalyst supported on mixed oxide of cerium and zirconium maintained an H2/CO ratio very close to 2 during the 10 hours of partial oxidation reaction. Samples containing manganese displayed smaller H2/CO ratios and lower performance in partial oxidation. / Uma das principais aplica??es do metano ? a produ??o de g?s de s?ntese, mistura de hidrog?nio e mon?xido de carbono. Os processos utilizados na produ??o de g?s de s?ntese a partir do metano s?o: reforma a vapor, reforma com CO2, oxida??o parcial e reforma autot?rmica. Neste trabalho, o comportamento de catalisadores de n?quel suportados em ?xidos mistos de c?rio e mangan?s na rea??o de oxida??o parcial do metano foi avaliado e comparado com o catalisador de n?quel suportados no ?xido misto de c?rio e zirc?nio. Os ?xidos mistos de c?rio e zirc?nio ou c?rio e mangan?s foram sintetizadas usando dois diferentes m?todos de prepara??o; o de precursores polim?ricos baseado no processo Pechini e por rea??o de combust?o usando um micro-ondas, seguido da impregna??o de n?quel com teor de 15 %. As amostras foram calcinadas a 300, 800 e 900 ?C e caracterizados por ?rea espec?fica (ASE), fluoresc?ncia de raios X (FRX), difra??o de raios X (DRX), microscopia eletr?nica de varredura (MEV), redu??o ? temperatura programada (RTP) e a rea??o de oxida??o parcial do metano. As ?reas espec?ficas das amostras diminuem com o aumento da temperatura de calcina??o e ap?s a impregna??o com n?quel. A solu??o s?lida c?rio-metal foi formada e nos composto com as maiores quantidades de ?xidos de mangan?s verificou-se a presen?a de outras esp?cies de mangan?s fora da estrutura da solu??o s?lida. Quanto ? microscopia eletr?nica de varredura os suportes a base de c?rio e zirc?nio preparados via Pechini exibem part?culas aglomeradas, sem geometria uniforme e sem a visualiza??o de poros na superf?cie, enquanto os compostos contendo mangan?s apresentaram alguns vazios na sua estrutura. Atrav?s da s?ntese por rea??o de combust?o a morfologia adquirida independente da composi??o proposta apresentou uma maior porosidade em rela??o ? s?ntese Pechini. Mesmo sendo os catalisadores preparados por diferentes m?todos de s?ntese, a inser??o de n?quel deixou seus perfis de redu??o (RTP) muito semelhantes. Para os catalisadores de n?quel suportados no ?xido misto de c?rio e zirc?nio, h? em primeiro lugar redu??o de esp?cies NiO que apresentam certa intera??o com o suporte, seguido da redu??o de Ce4+ em Ce3+ superficiais, com posterior redu??o do bulk. Para os catalisadores contendo mangan?s h? a redu??o das esp?cies de ?xido de n?quel, seguido de duas etapas de redu??o para as esp?cies Mn2O3 em Mn3O4 e Mn3O4 em MnO, com posterior redu??o do bulk. Quanto ?s rea??es de oxida??o parcial, o catalisador de n?quel suportados no ?xido misto de c?rio e zirc?nio preparado via m?todo Pechini, apresentou uma convers?o de CH4 de cerca de 80 %, sendo 81 % a convers?o quando preparado via combust?o. Esse comportamento manteve-se durante 10 horas de rea??o. Observou-se tamb?m que o teor de mangan?s influencia diretamente na atividade catal?tica dos materiais, quanto maior o teor de ?xido de mangan?s mais r?pido o catalisador apresentava desativa??o e desestabiliza??o. Para ambos os m?todos de s?ntese o catalisador de n?quel suportados no ?xido misto de c?rio e zirc?nio manteve a raz?o H2/CO bem pr?xima de 2 durante as 10 horas em que ocorre a rea??o de oxida??o parcial. As amostras contendo mangan?s apresentaram menores raz?es de H2/CO e menor desempenho na oxida??o parcial.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

Made available in DSpace on 2014-12-17T14:06:55Z (GMT). No. of bitstreams: 1 AnaPP.pdf: 5176837 bytes, checksum: 9d8890c4a2dd055dfe7d581f34a7f4e8 (MD5) Previous issue date: 2011-01-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Nickel-based catalysts supported on alumina have been widely used in various reactions to obtain synthesis gas or hydrogen. Usually, higher conversion levels are obtained by these catalysts, however, the deactivation by coke formation and sintering of metal particles are still problems to be solved. Several approaches have been employed in order to minimize these problems, among which stands out in recent years the use of additives such as oxides of alkali metals and rare earths. Similarly, the use of methodologies for the synthesis faster, easier, applicable on an industrial scale and to allow control of the microstructural characteristics of these catalysts, can together provide the solution to this problem. In this work, oxides with spinel type structure AB2O4, where A represents divalent cation and B represents trivalent cations are an important class of ceramic materials investigated worldwide in different fields of applications. The nickel cobaltite (NiCo2O4) was oxides of spinel type which has attracted considerable interest due to its applicability in several areas, such as chemical sensors, flat panel displays, optical limiters, electrode materials, pigments, electrocatalysis, electronic ceramics, among others. The catalyst precursor NiCo2O4 was prepared by a new chemical synthesis route using gelatine as directing agent. The polymer resin obtained was calcined at 350?C. The samples were calcined at different temperatures (550, 750 and 950?C) and characterized by X ray diffraction, measurements of specific surface area, temperature programmed reduction and scanning electron microscopy. The materials heat treated at 550 and 750?C were tested in the partial oxidation of methane. The set of techniques revealed, for solid preparations, the presence of the phase of spinel-type structure with the NiCo2O4 NixCo1-xO solid solution. This solid solution was identified by Rietveld refinement at all temperatures of heat treatment. The catalyst precursors calcined at 550 and 750?C showed conversion levels around 25 and 75%, respectively. The reason H2/CO was around 2 to the precursor treated at 750?C, proposed reason for the reaction of partial oxidation of methane, one can conclude that this material can be shown to produce synthesis gas suitable for use in the synthesis Fischer-Tropsch process / Catalisadores a base de n?quel suportados em alumina, t?m sido amplamente empregados nas diversas rea??es para obten??o de g?s de s?ntese ou hidrog?nio. Normalmente, altos n?veis de convers?o s?o obtidos por estes catalisadores, entretanto, a desativa??o por forma??o de coque e sinteriza??o das part?culas met?licas s?o ainda problemas a serem solucionados. Diversas abordagens t?m sido empregadas com a finalidade de minimizar estes problemas, dentre as quais tem se destacado nos ?ltimos anos a utiliza??o de aditivos como ?xidos de metais alcalinos e metais terras raras. Paralelamente, o uso de metodologias de s?nteses mais r?pidas, f?ceis, aplic?veis em escala industrial e que permitam o controle das caracter?sticas microestruturais destes catalisadores, pode em conjunto, prover a solu??o para este problema. Neste trabalho, ?xidos com estrutura tipo espin?lio AB2O4, onde A representa c?tions divalentes e B representa c?tions trivalentes, s?o uma classe importante de materiais cer?micos mundialmente investigados em diferentes campos de aplica??es. As cobaltitas de n?quel (NiCo2O4) s?o ?xidos do tipo espin?lio que tem atra?do consider?vel interesse devido a sua aplicabilidade em diversas ?reas, como em sensores qu?micos, monitores de tela plana, limitadores ?pticos, materiais para eletrodos, pigmentos, eletrocat?lise, cer?micas eletr?nicas, entre outras. O precursor catal?tico NiCo2O4 foi preparado por uma nova rota de s?ntese qu?mica usando a gelatina como agente direcionador. A resina polim?rica obtida foi tratada termicamente a 350?C. As amostras foram calcinadas em diferentes temperaturas 550, 750 e 950?C e caracterizadas por difra??o de raios X, medidas de ?rea superficial espec?fica, redu??o a temperatura programada e microscopia eletr?nica de varredura. Os materiais tratados termicamente a 550 e 750?C foram testados na oxida??o parcial do metano. O conjunto de t?cnicas revelaram, nos s?lidos preparados, a presen?a da fase de estrutura espin?lio do tipo NiCo2O4 juntamente com a solu??o s?lida NixCo1-xO. Esta solu??o s?lida foi identificada atrav?s do refinamento Rietveld em todas as temperaturas de tratamento t?rmico. Os precursores catal?ticos calcinados a 550 e 750?C apresentaram n?veis de convers?o em torno de 25 e 75%, respectivamente. A raz?o H2/CO foi em torno de 2 para o precursor tratado a 750?C, raz?o proposta pela rea??o de oxida??o parcial do metano, pode-se concluir que este material pode ser indicado para produzir g?s de s?ntese adequado para ser utilizado na s?ntese de Fischer-Tropsch

Made available in DSpace on 2014-12-17T14:07:05Z (GMT). No. of bitstreams: 1 DanieleMHM_TESE.pdf: 1582500 bytes, checksum: bba4e28b78ed6df0658bf0c3609ea506 (MD5) Previous issue date: 2011-02-21 / Nickel-bases catalysts have been used in several reform reactions, such as in the partial oxidation of methane to obtain H2 or syngas (H2 + CO). High levels of conversion are usually obtained using this family of catalysts, however, their deactivation resulting from carbon deposition still remains a challenge. Different approaches have been tested aiming at minimizing this difficulty, including the production of perovskites and related structures using modern synthesis methods capable of producing low cost materials with controlled microstructural characteristics at industrial scale. To establish grounds for comparison, in the present study LaNixFe1-xO3 (x=0, 0.3 or 0.7) perovskites were prepared following the Pechini method and by microwave assisted self-combustion. All samples were sub sequently calcined at 900 ?C to obtain the target phase. The resulting ceramic powders were characterized by thermogravimetric analysis, infrared spectroscopy, X ray diffraction, specific area and temperature programmed reduction tests. Calcined samples were also used in the partial oxidation reaction of methane to evaluate the level of conversion, selectivity and carbon deposition. The results showed that the calcined samples were crystalline and the target phase was formed regardless of the synthesis method. According to results obtained by Rietveld refinement, we observed the formation of 70.0% of LaNi0.3Fe0.7O3 and 30.0% of La2O3 for samples LN3F7-900- P, LN3F7-900-M and 41,6% of LaNi0.7Fe0.3O3, 30.7% of La2NiO4 and 27.7% of La2O3 for samples LN7F3-900-P and LN7F3-900-M.Temperature-programmed profiles of the LaNiO3 sample revealed the presence of a peak around 510 ?C, whereas the LaFeO3 sample depicted a peak above 1000?C. The highest l evel of methane conversion was obtained for LaNiO3 synthesized by the Pechini method. Overall, catalysts prepared by the Pechini method depicted better conversion levels compared to those produced by microwave assisted self-combustion / Catalisadores a base de n?quel t?m sido empregados em diversos tipos de rea??es de reforma, inclusive na oxida??o parcial do metano para obten??o de H2 ou g?s de s?ntese (H2 + CO). Normalmente, altos n?veis de convers?o s?o obtidos por estes catalisadores, entretanto, a desativa??o por deposi??o de carbono ainda ? um problema a ser solucionado. Diversas abordagens t?m sido empregadas no intuito de minimizar este problema, dentre as quais tem se destacado nos ?ltimos anos a utiliza??o de ?xidos com estrutura perovisquita e/ou estruturas relacionadas. Paralelamente, o uso de metodologias de s?nteses mais r?pidas, f?ceis, aplic?veis em escala industrial e que permitam o controle das caracter?sticas microestruturais destes catalisadores, pode em conjunto, prover a solu??o para este problema. A n?vel de compara??o perovisquitas do tipo LaNixFe1-xO3 (x=0, x=0,3 e x=0,7) foram preparados por dois m?todos: precursores polim?ricos (pechini) e autocombust?o assistida por microondas. Todas as amostras foram calcinadas a 900 ?C/4h para obten??o das fases desejadas. Os p?s-obtidos foram caracterizados por an?lise termogravim?trica, espectroscopia na regi?o do infravermelho, difra??o de raios-X, medidas de ?rea superficial especifica, redu??o ? temperatura programada. As amostras calcinadas foram testadas na rea??o de oxida??o parcial do metano, sendo avaliados os respectivos n?veis de convers?o, seletividade e a resist?ncia ? deposi??o de carbono. Ap?s calcina??o a fase desejada foi obtida para todas as amostras independente do m?todo de s?ntese, sugerindo claramente a forma??o de p?s cristalinos. De acordo com o resultados obtidos pelo refinamento Rietveld, observou-se a forma??o de 70,0% de LaNi0,3Fe0,7O3 e 30,0 % de La2O3 para as amostras LN3F7-900-P e LN3F7-900-M e 41,6% de LaNi0.7Fe0.3O3; 30,7% de La2NiO4 e 27,7 % de La2O3 para as amostras LN7F3-900-P e LN7F3-900-M. Os perfis de redu??o ? temperatura programada da amostra LaNiO3 apresentou pico de redu??o em torno de 510 ?C, j? a amostra LaFeO 3 apresentou pico de redu??o acima de 1000?C. Dentre os catalisadores estudados o que apresentou maior n?vel de convers?o de metano foi LaNiO3 obtido pelo m?todo pechini, de uma maneira geral os catalisadores obtidos pelo m?todo pechini apresentaram melhores resultados de convers?o que os catalisadores obtidos pela autocombust?o assistida por microondas

abstract: In-situ environmental transmission electron microscopy (ETEM) is a powerful tool for following the evolution of supported metal nanoparticles under different reacting gas conditions at elevated temperatures. The ability to observe the events in real time under reacting gas conditions can provide significant information on the fundamental processes taking place in catalytic materials, from which the performance of the catalyst can be understood. The first part of this dissertation presents the application of in-situ ETEM studies in developing structure-activity relationship in supported metal nanoparticles. In-situ ETEM studies on nanostructures in parallel with ex-situ reactor studies of conversions and selectivities were performed for partial oxidation of methane (POM) to syngas (CO+H2) on Ni/SiO2, Ru/SiO2 and NiRu/SiO2 catalysts. During POM, the gas composition varies along the catalyst bed with increasing temperature. It is important to consider these variations in gas composition in order to design experiments for in-situ ETEM. In-situ ETEM experiments were performed under three different reacting gas conditions. First in the presence of H2, this represents the state of the fresh catalyst for the catalytic reaction. Later in the presence of CH4 and O2 in 2:1 ratio, this is the composition of the reacting gases for the POM reaction and this composition acts as an oxidizing environment. Finally in the presence of CH4, this is the reducing gas. Oxidation and reduction behavior of Ni, Ru and NiRu nanoparticles were followed in an in-situ ETEM under reacting gas conditions and the observations were correlated with the performance of the catalyst for POM. The later part of the dissertation presents a technique for determining the gas compositional analysis inside the in-situ ETEM using electron energy-loss spectroscopy. Techniques were developed to identify the gas composition using both inner-shell and low-loss spectroscopy of EELS. Using EELS, an "operando TEM" technique was successfully developed for detecting the gas phase catalysis inside the ETEM. Overall this research demonstrates the importance of in-situ ETEM studies in understanding the structure-activity relationship in supported-metal catalysts for heterogeneous catalysis application. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2011

Die Nutzung fossiler Energieträger hat die wirtschaftliche und gesellschaftliche Entwicklung der Menschheit bedeutend geprägt. Die Relevanz der verschiedenen Brennstoffe ist dabei stark vom technologischen Niveau abhängig gewesen. Mit der fortschreitenden Entwicklung und dem Aufstreben der Automobilindustrie in der ersten Hälfte des 20. Jahrhunderts gewann Erdöl als Quelle für verschiedene Kraftstoffe und Grundchemikalien immer größere Bedeutung. Der Energieverbrauch der Industriestaaten ist seit dem stetig gestiegen und zum Ende des 20. Jahrhunderts treten immer mehr Schwellenländer wie China, Indien oder Brasilien mit großem Energiehunger in Erscheinung. Dadurch wurden die Vorkommen fossiler Brennstoffe mit immer höherem Tempo ausgebeutet, sodass Schätzungen davon ausgehen, dass bereits 2030 nur noch 75% des Bedarfs durch bereits erschlossene Lagerstätten gedeckt werden können.[1] Im Gegensatz dazu sind die Reserven an Erdgas noch deutlich größer. Erdgas besteht vor allem aus Methan, welches auch über alternative Methoden z.B. Biofermentation hergestellt werden kann. Neben der Nutzung als primärer Energieträger ist Methan Ausgangsstoff für die Herstellung einer Vielzahl chemischer Produkte, z.B. Methanol oder kurzkettige Olefine[2, 3]. Eine wichtige Zwischenstufe dieser Prozesse stellt die Herstellung von Synthesegas dar, einem Gemisch aus Wasserstoff und Kohlenmonoxid. Die Herstellung erfolgt industriell über die Reaktion von Methan und Wasserdampf, dem Steamreforming. Alternative Verfahren stellen die partielle Oxidation von Methan und das Dry Reforming dar. In dieser Arbeit wurde die Aktivität verschiedener Katalysatorsysteme in der Totaloxidation, der partiellen Oxidation und dem Dry Reforming von Methan untersucht. Zur Synthese der Katalysatoren wurde die von E.Kockrick[4, 5] entwickelte Mikroemulsionsmethode angewandt. Dabei wurde die Abhängigkeit der katalytischen Aktivität von der Zusammensetzung der Komposite und den Synthesebedingungen untersucht. Das modulare Syntheseprinzip der Mikroemulsionsmethode wurde durch die Substitution der katalytisch aktiven Spezies durch verschiedene Übergangsmetalle und Gemische demonstiert. Weiterhin wurde eine neue Methode zur Herstellung makroporöser SiC-Keramiken (Abbildung 1) entwickelt. Dabei wird ein flüssiges Polycarbosilan in einer Emulsion mit besonders hohem Anteil der inneren Phase (high internal phase emulsion = HIPE) polymerisiert und zum SiC umgesetzt. Diese SiC-PolyHIPEs zeichnen sich durch ihre hohe Porosität und geringe Dichte aus. Ausgehend von der Synthesevorschrift nach Schwab et al.,[6] die die Synthese styrolbasierter PolyHIPEs beschreibt, wurde Styrol schrittweise durch SMP-10 ersetzt. Die erfolgreiche Inkorporation wurde durch thermogravimetrische Untersuchungen nachgewiesen. Zur Vernetzung des HIPE wurden verschiedene Initiatoren verwendet. Über den Anteil des SMP-10 am PolyHIPE konnte direkt Einfluss auf den Porenradius und die Dichte genommen werden, wobei die Porosität konstant bei 75% gehalten werden konnte.[7] Das Potential der SiC-PolyHIPEs für den Einsatz als poröser Katalysatorträger konnte durch die Funktionalisierung mit CeO2 und den Einsatz in der temperaturprogrammierten Oxidation von Methan nachgewiesen werden. Bereits durch eine Beladung des SiC-PolyHIPEs mit 30 Gew.% CeO2 konnte die gleiche Umsetzungstemperatur des Methans erreicht werden wie bei reinem CeO2. Eine weitere Strategie zur Erzeugung katalytisch aktiver SiC-Materialien wurde über die Funktionalisierung des Polycarbosilans mit hydrophoben CeO2-Nanopartikeln und Cerkomplexen entwickelt. Dabei zeigte sich, dass durch das Einbringen von 5 Gew.% über Dodecylamin stabilisierter CeO2-Nanopartikel eine ähnliche Aktivität in der Methanoxidation erreicht wurde, wie mit reinem Cerdioxid. Die Funktionalisierung des SMP-10 mit Cerkomplexen ergab für alle Cerkomplexe eine Phasenseparation nach dem Entfernen des Lösungsmittels. Nach der getrennten Pyrolyse der Phasen konnte nur im Pyrolysat der festen Phase Cer nachgewiesen werden, wodurch die Methanoxidation katalysiert wird. Als weitere Methode zur Erzeugung katalytisch aktiver und poröser SiC-Komposite wurde die von E.Kockrick entwickelte inverse Mikroemulsionsmethode[4, 5] verwendet. Die gewonnenen CeO2/Pt-SiCKomposite zeigten spezifische Oberflächen von bis zu 482m²/g bei einer Pyrolysetemperatur von 840 °C. Bei höheren Pyrolysetemperaturen von 1200 bzw. 1500 °C wurden Komposite mit maximal 428 bzw. 87m²/g erhalten. Die katalytischen Untersuchungen der CeO2/Pt-SiC-Komposite erfolgten an einem selbst entwickelten Katalyseteststand mit online-Analytik.[8] Dabei wurden die Totaloxidation, die partielle Oxidation und das Dry Reforming von Methan untersucht. Die Umsetzungstemperatur in der Totaloxidation von Methan konnte um bis zu 443K abgesenkt werden. In der partiellen Oxidation von Methan, wie auch beim Dry Reforming konnte bereits ab einer Reaktortemperatur von 805 °C Umsätze gemäß dem thermodynamischen Gleichgewicht erreicht werden. Die Aktivität in der partiellen Oxidation ist vor allem abhängig vom Platingehalt im Komposit. Die höchste Aktivität war bei den Kompositen mit niedriger Pyrolysetemperatur zu verzeichnen. Nach der Pyrolyse bei 1500 °C hingegen wurden aufgrund der geringeren spezifischen Oberfläche und der damit einhergehenden verminderten Zugänglichkeit der aktiven Zentren geringere Umsätze beobachtet. Einen guten Kompromiss zwischen Oxidationsbeständigkeit und katalytischer Aktivität stellten hier die Komposite dar, die bei 1200 °C pyrolysiert wurden. Mit diesen Kompositen wurden ab 805 °C bis zu 90% Umsatz und 80% Selektivität zu CO in der partiellen Oxidation von Methan und im Dry Reforming erreicht. Beim wiederholten Einsatz der CeO2/Pt-SiC-Komposite in der temperaturprogrammierten Oxidation von Methan konnte nach über 7 Zyklen keine Deaktivierung des Katalysators beobachtet werden. Die Übertragbarkeit der Mikroemulsionsmethode konnte durch den Einsatz verschiedener anderer Katalysatormaterialien gezeigt werden. Die katalytische Aktivität der erhaltenen porösen MI/MII-SiCKomposite wurde in der temperaturprogrammierten Oxidation von Methan mit einer Absenkung der Onsettemperatur um 177K bis 267K bestimmt. Damit stellt die Mikroemulsionsmethode eine flexible und robuste Möglichkeit zur Herstellung poröser SiC-Komposit-Katalysatoren dar. Literatur [1] International Energy Agency; World Energy Outlook, 2010. [2] M. Stöcker, Microporous Mesoporous Mater., 1999, 29(1-2), 3–48. [3] A.P.E. York, T. Xiao, M.L.H. Green, and J.B. Claridge, Catal. Rev. - Sci. Eng., 2007, 49(4), 511 – 560. [4] E. Kockrick, P. Krawiec, U. Petasch, H.-P. Martin, M. Herrmann, and S. Kaskel, Chem. Mater., 2008, 20(1), 77–83. [5] E. Kockrick, R. Frind, M. Rose, U. Petasch, W. Böhlmann, D. Geiger, M. Herrmann, and S. Kaskel, J. Mater. Chem., 2009, 19(11), 1543–1553. [6] M.G. Schwab, I. Senkovska, M. Rose, N. Klein, M. Koch, J. Pahnke, G. Jonschker, B. Schmitz, M. Hirscher, and S. Kaskel, Soft Matter, 2009, 5(5), 1055. [7] R. Frind, M. Oschatz, and S. Kaskel, J. Mater. Chem., 2011, (in Revision). [8] R. Frind, L. Borchardt, E. Kockrick, L. Mammitzsch, U. Petasch, M. Herrmann, and S. Kaskel, Appl. Catal., A, 2011, (in Revision).